The former Blues boss has been back to Stamford Bridge on two occasions this season, with a humbling setback suffered in the Premier League along with a FA Cup quarter-final exit.
He will get the opportunity to make amends at Old Trafford this weekend, but table-topping Chelsea will arrive in a confident mood and aware that midweek European exertions could sap energy from their fierce rivals.
Alonso told Standard Sport: "It will be tougher this time around. They are one of the best teams in England, no doubt. It will be a very hard game, even more so after losing twice against us.
"They will give even more to try and beat us. We will have to do the same or more than before to get another win.
"They’re playing at Anderlecht tonight but they have a big squad, full of good players.
"They will be hard to beat, no matter who they pick or the fact they’re playing in the Europa League just three days before. We will have to be ready."
Chelsea’s recent record at Old Trafford suggests that they will cause Mourinho’s men plenty of problems.
Unfortunately for United, who have been held on eight occasions at home this season, there has been a tendency for stalemates to be played out between two heavyweight outfits in Manchester.
Four of their last five meetings have ended all square, with Chelsea prevailing 1-0 in the other fixture on that list.
Antonio Conte will lead his troops into battle this weekend sat seven points clear at the top of the table and fast closing in on title success in his first season at the helm.